Enhancing heat exchanger performance through hybrid angle of attack control for drop-shaped tubes

In this study, a numerical investigation was conducted to explore the potential improvement in the overall performance of heat exchangers comprising drop-shaped tubes through the control of the angle of attack. A comprehensive analysis was conducted, evaluating eight distinct configurations of 20-row bundles consisting of drop-shaped tubes in both staggered and in-line arrangements. A thorough comparison was made against corresponding bundles with circular tubes. The study covered a range of Reynolds numbers Re = 1.78 × 103–1.87 × 104 and angles of attack θi−j = 0°–360°. Two methods were employed to evaluate the thermal-hydraulic performance. The findings indicated that the friction factor of case 6 of drop-shaped tube bundle (θ1−5 = 0°, θ6−10 = 330°, θ11−15 = 30°, θ16−20 = 0°) exhibited a reduction of approximately 27%–43% and 42%–46% compared to the staggered (case 3) and in-line (case 1) configurations of drop-shaped tube bundles at zero angles of attack, respectively. Additionally, case 6 achieved the highest thermal-hydraulic performance, surpassing the staggered bundles of circular tubes (case 3) by 1.4–1.8 times and the in-line bundles of circular tubes (case 1) by 2.9–3.5 times. Novel equations were derived to estimate the mean Nusselt number, effectiveness, and friction factor for case 6, exhibiting a maximum deviation of 0.74%, 0.48%, and 0.73% correspondingly.